a b s t r a c tMiniature photobioreactors (mPBr) represent a potential platform technology for the high-throughput, phototrophic cultivation of microalgae. This work describes the development and characterisation of a novel orbitally shaken twin-well mPBr, and its scale-out to a 24-well microplate format, suitable for optimisation of microalgae culture conditions. Fluid hydrodynamics, oxygen mass transfer coefficient (k L a) and light intensity distribution in the mPBr were first investigated as a function of orbital shaking frequency. High speed video analysis of the shaken wells indicated rapid fluid flow and good mixing while measured k L a values varied between 20 and 80 h −1 . Light intensity variation across the scaledout platform was in the range ±20 mol m −2 s −1 . The use of the mPBr platform was demonstrated for optimisation of conditions for the batch cultivation of Chlorella sorokiniana. Using a modified tris-base phosphate (TBP) medium, the highest biomass concentration and productivity achieved were 9.2 g L −1 and 2.5 ± 0.2 g L −1 d −1 respectively at 5% CO 2 with a light intensity of 380 mol m −2 s −1 . In general, cell growth rate and yield increased with increasing shaking frequency (up to 300 rpm) while culture conditions had limited impact on pigment production. Overall, these results demonstrate the application of the mPBr for rapid optimisation of phototrophic culture conditions and establishment of high cell density cultures.
Purpose A novel cost-effective bio-digester was explored to convert biological waste into useful clean energy. The bioreactor was aimed to anaerobically digest locally sourced cow dung and chicken droppings. Design/methodology/approach The design consideration is a batch horizontal 267 L digester made from cast iron with centrally positioned four-impeller shaft to enhance mixing. The system operated with a retention time of 63 days and a substrate (cow dung and poultry waste) ratio of 1:2 and water substrate ratio of 1:0.5 in the gasholder system. The purification, compression and performance evaluation of the generated biogas were also conducted. Findings The total volume of gas produced for each substrate compositions designed over 14 days ranges between 49.34 and 52.91 mL/day. The optimal value of 52.45 ml using cow dung and poultry waste (w/w) 20:80 was obtained. The average ambient temperatures during the study were within the mesophilic range of 20-40°C. The pH values were stable and always in the optimal range of 6.5-8.0. The reductions in moisture content, ash content, total solids and volatile solids were from 80.50-0.20 per cent, 39.60-14 per cent, 18.50-5.90 per cent and 11.60-4.90 per cent, respectively. Originality/value The developed digester is cost-effective and would help minimize solid waste disposal. The estimated methane contents of the gas from cow dung and chicken waste after scrubbing were found to be 71.95 per cent and could be harnessed in solving the energy crisis in the developing nations.
In this early study, new cement-bonded bi-composite fibreboard (FB) was made from water hyacinth (WaHy) and waste paper (WP). Ordinary Portland cement (PdCe) used as a binder was mixed with other two additives: gypsum plasters (GyPl) and wood ash (WdAh), in defined proportions to form bonding matrices. The WP and WaHy were pre-treated and a linked process was developed for the mixing and consolidation steps. The FBs produced were based on different proportions of composites, binder, and additives mixed. The FBs produced were made from different proportions of composites, binders, and additives. Improved tensile strength was observed for bi-composite FB from WaHy mixed with WP. In general, FBs having densities in the range of 0.50-0.57 g cm −3 were compared favourably with the ASTM and ANSI standards (95%), thus making the FBs a potential alternative for building and construction purposes. More elaborate research with advanced analytical techniques is hereby suggested.
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